On Thu, Jul 24, 2025 at 07:15:12PM +0100, Andrew Bower wrote:

On Wed, Jul 23, 2025 at 10:31:47PM +0100, Andrew Bower wrote:

On Mon, Jun 30, 2025 at 11:36:59PM +0100, Andrew Bower wrote:

[...]
1. Unitialised 'sessions' variable is a a bug on all systems which leads
to a segfault on some. I'm now tagging this bug as having a patch.

In the absence of any other fixes, my patch for this still stands.
But...

2. elogind not being queried. Is this an elogind issue? Should it give a
different answer to sd_booted() or is this the wrong way to detect the
seat management capability? 'who' does not have this problem - it
somehow queries elogind anyway.

Removing the call to sd_booted() and just using the result of
sd_get_sessions() is sufficient. I get the correct outcome in this case.

Unfortunately we don't then get any runtime fallback to utmp but my
guess is working elogind support would be preferred (and should be fixed
for trixie).

I am not proposing a patch here because it needs attention from someone
more familiar with the relevant components.

My hunch is that the best plan for trixie is to go straight to calling sd_get_sessions() and not testing sd_booted(). This would then supersede
the patch for (1).

procps then resorts to utmp.

3. Some (vc) sessions not reported unless running as root, but the non-root
user could read utmp. 'who' does not have this problem but then it
probably didn't resort to reading utmp (see 2 above).

This was a mistake - ignore this: the additional session was caused by
sudo itself.

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On Sun, Jul 27, 2025 at 11:08:56PM +0100, Andrew Bower wrote:

On Thu, Jul 24, 2025 at 07:15:12PM +0100, Andrew Bower wrote:

On Wed, Jul 23, 2025 at 10:31:47PM +0100, Andrew Bower wrote:

On Mon, Jun 30, 2025 at 11:36:59PM +0100, Andrew Bower wrote:

[...]
1. Unitialised 'sessions' variable is a a bug on all systems which leads
to a segfault on some. I'm now tagging this bug as having a patch.

In the absence of any other fixes, my patch for this still stands.
But...

2. elogind not being queried. Is this an elogind issue? Should it give a
different answer to sd_booted() or is this the wrong way to detect the
seat management capability? 'who' does not have this problem - it
somehow queries elogind anyway.

Removing the call to sd_booted() and just using the result of sd_get_sessions() is sufficient. I get the correct outcome in this case.

Unfortunately we don't then get any runtime fallback to utmp but my
guess is working elogind support would be preferred (and should be fixed
for trixie).

I am not proposing a patch here because it needs attention from someone
more familiar with the relevant components.

My hunch is that the best plan for trixie is to go straight to calling sd_get_sessions() and not testing sd_booted(). This would then supersede
the patch for (1).

I think we should do this:

Remove sd_booted() check
if sd_get_sessions()
< 0 && != ENOENT: error
> 0: show sessions
default: fallback to utmp

This should deal with:
1. systemd and elogind with some login sessions: show sessions
2. neither systemd nor elogind: fallback to utmp reading
3. systemd and elogind with no sessions: show nothing, as now, but via
fallback utmp route with no practical difference.

I don't see a downside from this approach.

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On Mon, 28 Jul 2025 at 17:31, Andrew Bower <[email protected]> wrote:

I think we should do this:

Remove sd_booted() check
if sd_get_sessions()
< 0 && != ENOENT: error
> 0: show sessions
default: fallback to utmp

This should deal with:
1. systemd and elogind with some login sessions: show sessions
2. neither systemd nor elogind: fallback to utmp reading
3. systemd and elogind with no sessions: show nothing, as now, but via
fallback utmp route with no practical difference.

I don't see a downside from this approach.

I think this is the correct way too. I'll double check that 0 user path
because it looks odd, but its probably doing the right thing.

- Craig

<div dir="ltr"><div dir="ltr">On Mon, 28 Jul 2025 at 17:31, Andrew Bower &lt;<a href="mailto:[email protected]">[email protected]</a>&gt; wrote:</div><div class="gmail_quote gmail_quote_container"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.
8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I think we should do this:<br>

Remove sd_booted() check<br>
if sd_get_sessions()<br>
  &lt; 0 &amp;&amp; != ENOENT: error<br>
  &gt; 0: show sessions<br>
  default: fallback to utmp<br>

This should deal with:<br>
  1. systemd and elogind with some login sessions: show sessions<br>
  2. neither systemd nor elogind: fallback to utmp reading<br>
  3. systemd and elogind with no sessions: show nothing, as now, but via<br>      fallback utmp route with no practical difference.<br>

I don&#39;t see a downside from this approach.<br></blockquote><div>I think this is the correct way too. I&#39;ll double check that 0 user path because it looks odd, but its probably doing the right thing.</div><div><br></div><div> - Craig</div><div><br>
</div></div></div>

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Hi Craig,

Thanks for reviewing my suggestions!

On Mon, Jul 28, 2025 at 08:07:12PM +1000, Craig Small wrote:

On Mon, 28 Jul 2025 at 17:31, Andrew Bower <[email protected]> wrote:

I think we should do this:

Remove sd_booted() check
if sd_get_sessions()
� < 0 && != ENOENT: error
� > 0: show sessions
� default: fallback to utmp

This should deal with:
� 1. systemd and elogind with some login sessions: show sessions
� 2. neither systemd nor elogind: fallback to utmp reading
� 3. systemd and elogind with no sessions: show nothing, as now, but via
� � �fallback utmp route with no practical difference.

I don't see a downside from this approach.

I think this is the correct way too. I'll double check that 0 user path because
it looks odd, but its probably doing the right thing.

A slight tweak to this algorithm might allay anxiety about the 0
sessions case, whereby we reintroduce the sd_booted() check in a
different place to create an alternative path:

if sd_get_sessions()
< 0 && != ENOENT: error
> 0 || sd_booted(): show sessions
default: fallback to utmp

In this case if systemd is running then the utmp fallback is never
attempted - this results in no ambiguity about the outcome in this more predictable scenario.

(N.B. would also need to zero out the session count in case of ENOENT)

What do you think of this variation?

Andrew

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